With the recent rapid growth of wireless communication industry, it is desirable to provide a mobile terminal device that supports various wireless communication services based on various wireless communication standards. Types of wireless communication services include Long Term Evolution (LTE) standardized by the 3rd Generation Partnership Project (3GPP), Wireless Fidelity (WiFi) on the IEEE802.11 standard, Bluetooth on the IEEE802.15.1 standard, the Worldwide Interoperability for Microwave Access (WiMAX) on the IEEE802.16e standard, and the Global Positioning System (GPS) having a usage frequency band of 1.563 to 1.578 GHz.
The frequency band used for wireless signals transmitted and received between the mobile terminal device and other devices, such as a base station device, differs depending on the type of wireless communication service used. It is thus desirable to provide an antenna that may transmit and receive wireless signals over a wide frequency band in the mobile terminal device such that the mobile terminal device may support the many different types of wireless communication services.
Recently, mobile terminal devices have been reduced in size and in thickness. In order to further reduce the size and thickness of the mobile terminal device, it is desirable to also reduce the size and thickness of the antenna provided in the mobile terminal device.
As a related technology, a proposed antenna device includes a substrate, a radiation electrode, a grounding electrode, an impedance matching element, and a switch. The radiation electrode is provided on a substrate and is configured to transmit and receive wireless signals in a wider bandwidth. The grounding electrode is provided on a back surface of the substrate. A feeder wire is connected to the radiation electrode via a feeding point and is provided on the substrate. The impedance matching element is provided at a position of a predetermined distance from the feeding point. One end of the impedance matching element is connected with the grounding electrode arranged on the back surface, and the other end thereof is provided to be connected with the feeder wire via a switch in parallel with the radiation electrode. When the switch is operated in accordance with a predetermined control signal and the impedance matching element and the feeder wire are connected, impedance of the radiation electrode is matched by the impedance matching element with respect to a signal having a predetermined frequency.
As another related technology, a proposed antenna device includes a main antenna, an antenna adjusting unit, and a switching unit. The antenna adjusting unit is connected to one side of the main antenna having a fixed length. The antenna adjusting unit connects one or more sub antennas to the main antenna in accordance with transmission and reception quality (or change in the peripheral environment) of a terminal to change the length of the main antenna. The switching unit causes the switch to operate in accordance with the operating frequency band of the terminal and connects the main antenna or another antenna corresponding to a predetermined frequency band to a matching circuit.
As yet another related technology, a proposed antenna device includes a grounding conductor, a first antenna element, a second antenna element, and a feeding point. The first antenna element is an inverse L-shaped antenna constituted by a relatively short first side and a relatively long second side, and which operates with a resonance frequency of a fundamental mode and a higher mode. The feeding point is provided between the grounding conductor and the first side of the first antenna element. The second antenna element is an antenna of which one end is combined to the first side of the first antenna element. The second antenna element forms an inverse L-shape between the first antenna element and the feeding point. The second antenna element includes a first switch that may selectively change the antenna length of the second antenna element and a second switch that may selectively connect the feeding point and the second antenna element. The antenna device operates in different frequency bands in accordance with opening and closing of the first and the second switches.
Japanese Laid-open Patent Publication No. 2011-155626, Japanese Laid-open Patent Publication No. 2006-81181, and Japanese Laid-open Patent Publication No. 2009-76961 contain information further to the related art technology discussed above.